ENGINE BLOCK: Identifying the 65 400 block couldn't be simpler. At the front, on top, directly behind the water pump is the block casting number 389298B in big bold raised letters. It is found, just to the right of the oil pressure sending unit hole. The side view shows the large "B" at the rear right side of the block, ahead and above the oil filter. ( Note: in 66-67 the block number changed to 390925E ) There is NO VIN derivative on the 65 blocks. It was not added until 1968.

The views below show the location of the Julian Date at the top rear of the block next to the distributor hole.

ENGINE HEADS: Identifying the 65 400 heads is equally simple. There is a large raised "A" cast at the left side of both heads and the number 383821 below the valve cover, visible on both heads.

By the 1965 model year, Oldsmobile had the answer, by adding 35 additional horsepower. The General Motors brass were swayed by the success of the Pontiac GTO, so they relented on their decision to keep big blocks out of the mid-size cars. The 65 Cutlass 442 could now be equipped with a de-stroked version of Oldsmobile's monster Stage II 425 Rocket V8. Apparently modified to keep within the revised GM bounds restricting mid-size cars to engines of 400 cubic inches or less, this new 442 powerplant measured out at 400 cubic inches on the nose. Using what Hot Rod magazine described as a "moderate" 10.25:1 compression ratio, the 442's Rocket engine produced a claimed 345 horsepower and an amazing 440 pound-feet of peak torque at 3200 rpm. There's no substitute for cubes.

Designed for heavy-duty use, the engine offered such hot rod parts as forged steel crankshaft and connecting rods, light, stamped steel rocker arms with tubular pushrods, plus 2.0-inch intake and 1.625-inch exhaust valves. All of this good stuff, to use the words of Hot Rod, "contributed to vigorous and long-lasting health."

The short stroke 1965-67 400s are awesome engines. The early 400 engines rev higher than any other big block. They will rev higher than a 425. They have less piston mass. These things will turn almost 7000 RPM.

With the big-block engine under the hood the 442 had quickly come into its own. Oldsmobile still advertised the broad range of its vehicles with the mildly provocative slogan: "Pick the Rocket to fit your pocket!" But with the beefier engine, 442 now meant 400 cubic inches, 4-barrel carburetor and 2 exhausts.

A series of W30 options available on the 442 would do nothing but enhance the reputation of the car as the years passed. The first of these added a Tri-Power-like triple two-barrel carburetor set-up and forced cold-air induction which delivered what Olds said was 360 horsepower. Others suggest the true horsepower figure was more like 400. Before the demise of the 442, it would be equipped with a 455-cubic inch V8 of monstrous proportions that only made its legend more stellar.

The big and small block engine types are almost identical, with the big block having a higher deck than the small block. The bore centers are the same, since the only differences between the small-block and big-block Olds blocks are the deck height (9.33" and 10.625", respectively) and the main journal size ( 2.5" and 3.0"; diesel 350 used BB size mains, however ).

Many internal parts interchange, but it is best to keep the big block parts on the big block and the same for the small block.

The engines were sometimes named, and this was printed on the air cleaner label or sticker. Mid 60's 425s were known as Super Rockets. Some featured Ultra High Compression on their labels.

Quick Identification:

The large oil fill tube on the front of the engine, sticking up from the timing chain area, is a dead giveaway that it is an Olds engine.

Engine code on the oil filler tube.

400 V8 345 4-BBL MT 10.25:1 QW

400 V8 345 4-BBL AT 10.25:1 QR

400 V8 360 3 X 2's MT 10.25:1 QZ

The distributor is found at the back of the block and it does not go through the intake manifold, but right into the block. Also the spark plugs will be above the exhaust manifolds with no need for heat shields.

The Block Code and/or Head Code can give you an idea, but some codes cover many years. The casting number is ususally nearby. Other than that, there is no method of determining the year of manufacture of an Olds block.

The valve covers are a distinctive shape. Straight running front to rear, with an arc connecting each end of the two lines, to define front and rear. From their sealing surface, the covers are curved as they meet their top. The top of the covers are flat, like someone cut off the curved top.

The thermostat cover/radiator hose has a special molded in bypass pipe for the waterpump.

The day of the year of manufacture is the big number right by the distributor hole.

Original paint color can help identify an engine, or further identify it. However, since paint is easily changed, it should be used as supporting evidence, not as absolute indication of engine lineage.

The VIN derivative stamping or engine unit number is on the left most side of the block or head, on the driver's side, just below the cylinder head, toward the front, behind the power steering pump.. The pad is part of the engine and will indicate the year of manufacture, but that is usually rusted beyond recognition, and it can be changed by restamping. Basically it IDs the car in which the motor was originally installed. It can provide some circumstantial info but not a positive ID.

( Note: If the engine was replaced under warranty, the pad may be blank. Rubbing alcohol and Q-tips help to remove the grime and grit from the stamping. )

1964-67 V-8 Engine:

Code is stamped on the right cylinder head. Unfortunately, this only applies to what was originally the passenger side head. This code consists of a prefix letter (330 V-8=T (1964-65) or W (1966-67), 400 V-8 = V), then a production sequence number, followed by a suffix code letter ( L = Low compression, E = 2-bbl export, G = High compression, H = 4-bbl export ). A 2-letter code on the oil filler tube identified the engine.

Oldsmobile Generation 2 Engines:

3.1 330

3.1.1 Jetfire Rocket

3.2 400

3.2.1 4-4-2 Rocket

3.3 425

3.3.1 Super Rocket

3.3.2 Starfire

3.3.3 Toronado Rocket

Generation 2:

The second generation of Oldsmobile V8s was produced from 1964 through 1990. Most of these engines were very similar, using the same bore centers, although "big-block" versions were produced with a 10.625 in (269.9 mm) deck height rather than 9.33 in (237 mm). Big-block and Diesel versions also used a larger 3.0 in (76.2 mm) instead of 2.5 in (63.5 mm) main bearing journal for increased strength. All generation-2 small-block Olds V8s used a stroke of 3.385 in (86 mm). The big-block engines initially used a forged crankshaft with a stroke of 3.975" for the 1965-1967 425 and 400 CI versions; starting in 1968, both the 400 in³ and the 455 in³ big blocks used a stroke of 4.25 in (107.9 mm), with crankshaft material changed to cast iron except in a few rare cases.

These engines, while being a wedge-head, had a unique combustion chamber that resulted from a valve angle of only 6°. This was much flatter than the 23° of the small-block Chevrolet and 20° of the Ford small-block wedge heads. This very open and flat chamber was fuel efficient and had lower than average emissions output. It was the only GM engine to meet US emission standards using a carburetor all the way up to 1990.

400:

The 400 in³ ( 6.6 L ) version was the second tall-deck "big-block" Olds. Two distinct versions of the 400 CID engine were made:

1965 through 1967 Early 400's used a slightly over-square 4.000 in (101.6 mm) bore and 3.975 in (101.1 mm) stroke. All the pre-1968 engines used a forged steel crankshaft.

1968 and 1969 400's shared the Olds big-block standard 4.25 in (107.9 mm) stroke with the 455 but used a very undersquare 3.87 in (98.3 mm) bore to comply with GM's displacement restrictions in the A-body cars and reduce tooling costs. This Later 400 is considered by many enthusiasts to be less desirable because of the powerband characteristics induced by this exceedingly undersquare format, and the fact that the crankshafts were now made of less durable cast iron material. Early 400's used the same forged steel crankshaft as the 425's, while the Later 400's used the same cast iron crankshaft of the 455's, with rare exception- some 1968 and later Olds 400/455's were produced with forged steel crankshafts. These rare cranks can be readily spotted by the "J" shaped notch in the OD of the rear flange; cast iron cranks have a "C" shaped notch.

All 1965 thru 1969 Olds 400's were painted bronze ( not gold ).

Engine Casting Number Deciphering

This chart will help you decipher what engine type your have in your Cutlass. While the data is somewhat inconclusive, it provides an overall point of reference for engine decoding. If you have information to fill in the gaps or see an error, please contact me.

In order to figure out what block you have in your car, you must locate the Casting Number. This can be found at the front of the engine on a flat surface behind the timing chain area. ( See picture at top of page) Look to the right (if facing the fan) of the oil filler tube and you will see the stamping on the block. This number should match one of those below. Remember, big blocks are identified by a letter for the ID Code, while small blocks carry a number.

Big Block reference chart:

Casting NumberID CodeCIDYear(s) ProducedNotes

381917A4251965B Bodies (big cars) only

386525Red A 425

389298Bronze B4001965 One year only 442 motor. The lifter cam angle bank was 45 degrees

The engines in the 65 442 were painted Bronze only. The engine was painted after assembly, as complete units, less the alternator & power steering brackets, pulleys, fan, power steering pump, air conditioner pump (if equipped), and other accessories, which were installed after the paint was applied.

They were painted assembled, complete with heads, intake manifold, water pump, valve covers, and oil pan in place. The distributor, thermostat by pass hose and manual bell housing were also mounted and received some overspray in the process.

Best Matches:

Plasti-Kote color FM8069

Krylon AP-31 (if you can find it)

The engine unit number that is stamped on the front of the passenger side head can show that it is original to the car if you have the Protect-O-Plate. That same number appears on the Protect-O-Plate. Of course it is only on the one head, so technically it only proves one head is original. Same thru '67.

Early 400

Built 1965 - 1967.

Late 400

Built 1968 - 1969.

The short stroke 1965-67 400s were great engines, but in 68-69 Olds attempted to reduce emissions by using a reduced bore to minimize combustion chamber quench area and thus lower unburned hydrocarbons (emissions controls actually started in 1968 on 49-state cars). Note that this decision to go with a smaller bore was also due in no small part to the desire to use a common crankshaft with the new 455 in 1968 as well. The result is a terribly undersquare motor (3.870 bore x 4.125 stroke) which won't rev very well. This is the worst bore-to-stroke ratio of any American V8 from the modern era.

One limiting factor to your buildup will be the small bore size of your later 400, which can shroud larger valves. One great way to gain yourself some horsepower is to move up to a 455 shortblock with your stock "C" heads; more cubic inches, and the large valves will breathe even better.

The story on the change from the early 400 to the 68-69 400 was due to design changes to start limiting emissions and with the longer stroke they picked up more torque which lead to more power at lower rpm. Thus their early attempt to reduce gas consumption and increase mileage with lower emission. Plus the redesign of the internals which now shared the same crank and rods as the 455's.

I recall reading that the undersquare design of the 400 and 455 in 1968 was intended to reduce the quench area in the combustion chamber to reduce emissions. Apparently, the walls of the combustion chamber are cooler than the rest (makes sense) and fuel can condense out there and lead to incomplete burning and thus higher HC and CO emissions. By making the bore smaller, the surface area of the combustion chamber is, by definition, reduced.

Of course, while that was the published rationale, I suspect that this decision had more to do with commonality of the expensive crank forging between the 400 and 455 than anything else. Since Olds likely expected to sell many more 455s than 400s, redesigning the 400 to use the 455 crank and rods probably made a lot of financial sense.